It is known that mechanisms for controlling the volume in audio instruments are classified into analog type and electronic type.
The analog type volume controller controls the level of volume (which is referred to "sound volume" herein) by using a variable resistor which can adjust the level of signal for regulating the sound volume. Normally, the variable resistor is adjusted by rotating a knob to an angular position corresponding to the desired sound volume.
On the other hand, a setting of sound volume has been digitized and stored in a memory. The sound volume can be adjusted when a preselected digital value is added to or subtracted from the stored value.
Such a type of electronic volume controllers are disclosed, for example, in Japanese Utility Model Laid-Open No. Sho 57-88316, Utility Model Laid-Open No. Sho 59-140520, Utility Model Laid-Open No. Sho 61-158723, Patent Laid-Open No. Sho 61-242407, Patent Laid-Open No. Sho 62-21315, Patent Laid-Open No. Sho 64-10713, Patent Laid-Open No. Sho 64-36111, Patent Laid-Open No. Sho 64-81512, Utility Model Laid-Open No. Hei 1-72718, Patent Laid-Open No. Hei 1-143511 and Patent Laid-Open No. Hei 1-143512.
The electronic volume controller generally comprises an operation button for increasing the sound volume (which will be referred to as "UP key") and another operation button for decreasing the sound volume (which will be referred to as "DOWN key"). When the UP key or DOWN key is once turned off immediately after it has been turn on (this operation will be referred to as "single operation"), the preselected value is once added to or subtracted from the setting value of sound volume stored in the memory. Thus, the sound volume will be increased or decreased by a given amount of volume change. Such a volume control mode will be referred to as "single operation mode".
The electronic volume controllers frequently have such a function that when the UP key or DOWN key is maintained at its ON state for a time period exceeding a preselected time period (this operation will be referred to as "continuous operation"), the preselected value is added to or subtracted from the setting value of sound volume stored in the memory at each unit time so as to increase or decrease the sound volume by an amount of volume change at each unit time until the UP key or DOWN key is turned off. This volume control mode will be referred to as "continuous operation mode".
However, the conventional electronic volume controllers are disadvantageous in that they are inferior in operability to the analog type volume controller.
The analog type volume controller is very easy to be operated since a desired sound volume can be obtained merely by rotating a knob, as described above. More particularly, an operator is only required to rotate the knob rapidly to a position near a desired sound volume level and then to rotate the knob gradually to a position accurately corresponding to the desired sound volume level.
The electronic volume controller uses the continuous operation mode when it is desired to increase or decrease the sound volume rapidly to a position near a desired sound volume. When such a position is reached, both the UP and DOWN keys are used to fine adjust the sound volume in the single operation mode. In such a time, the sound volume will not be adjusted depending on the sense of the operator's finger(s), unlike the analog type volume controller. Therefore, it cannot be avoided that the operator feels cumbersome in handling the electronic volume controller for such a reason why the operator cannot sensuously detect the accurate relationship between the key operation and the volume change in each of the single and continuous operation modes.
There is further known an electronic volume controller which can be adjusted by a rotatable knob. Since such a rotatable knob extends outwardly from the console panel of the controller, the knob frequently provides any obstruction. It is thus desired that the electronic volume controller can have UP and DOWN keys capable of adjusting the sound volume in conformity with the human's sense.
It is therefore an object of the present invention to provide an electronic volume controller improved in operability.